Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$28.40	12.180%	$31.8591	$31.86	$31.85	$31.90
Purchase #2	$227.91	12.652%	$256.7452	$256.75	$256.75	$256.70
Purchase #3	$37.52	12.836%	$42.3361	$42.34	$42.35	$42.30
Purchase #4	$224.71	12.778%	$253.4234	$253.42	$253.40	$253.40
Purchase #5	$181.36	4.711%	$189.9039	$189.90	$189.90	$189.90
Purchase #6	$207.60	10.626%	$229.6596	$229.66	$229.65	$229.70
Purchase #7	$59.37	9.820%	$65.2001	$65.20	$65.20	$65.20
7 purchase totals =	$966.87		$1,069.1274	$1,069.13	$1,069.10	$1,069.10